Biometrics is commonly used to identify and/or authenticate persons based on individual physical characteristics.
Such an identification via biometrics, implemented by a biometric authentication system, comprises the three following main steps:                capturing of a reference biometric sample coming from the authorized person (for example a reference image of an authorized person);        creation of a reference file, or “reference signature” (which comprises at least one characteristic element of the reference image), by a specific treatment applied to the reference biometric sample, then storage of this reference file;        verification wherein, in the same way as with the aforementioned steps of capturing and of creating, a capture of a biometric sample to be compared coming from the person to be authenticated and the creation of a file to be compared, or “signature to be compared” is carried out, then a comparison of the reference file with the file to be compared in order to determine their rate of similarity and take the decision that is required.        
As such, the information stored is not biometric samples, but mathematical models of these samples that distinguish one biometric sample from another. This model is called a “signature” or a “template”.
The creation of a reference signature is carried out during a phase referred to as enrolment (or learning) that groups together the steps of capturing the reference biometric sample, creating and storing the reference signature and storing the information on the identity of the person such as his last name, first name, identifier (personal identification number).
The authentication of a person via biometrics can in particular be based on the measurement (or capture) of at least one of the following biometric samples:                his fingerprint;        his palm print (hand print);        the print of his retina;        the print of his iris;        the print of his face (the form of a face);        etc.        
There are biometric authentication systems based on a chip card reader integrating a biometric sensor (for example a fingerprint sensor) and a specialized processor.
According to this known technique, the reference print (or reference image) of the authorized user is stored in the chip of the card and the verification is carried out in the terminal, using the data of this chip card. When the reference print stored in the card agrees with the print to be compared (of the user to be authenticated) captured by the sensor, the card is unlocked and, for example, then authorizes secure electronic transactions.
However, a disadvantage of such a biometric authentication system is due to the fact that the step of verification (wherein the reference signature is compared with the signature to be compared in order to authenticate a user to be authenticated) is implemented in the chip card reader. Consequently, the signatures associated with the prints must be stored at least momentarily in the reader. They can therefore be hacked, altered and/or re-used (“replayed”) fraudulently using the reader by an ill-intentioned user.
There are also biometric authentication systems (such as described in for example the document entitled “Biométrie: la verification se fait maintenant dans la carte Java; (Biometrics: the verification is now done in the Java card)” published in “Electronique international Hebdo” on 16 Dec. 1999 under number 373) wherein a chip card, provided with a biometric sensor (for example a thermal print sensor), itself carries out the step of verification. It is then the card that compares the reference signature (corresponding to the reference print) with the signature to be compared (corresponding to the print to be compared), without the latter leaving the card.
As such, because the creation, storage and comparison of the signatures are carried out in the chip card, the reference signatures and the signatures to be compared do not transit by a reading terminal of the chip card (chip card reader, automated teller machine, etc.) the aforementioned problems of authentication security are for the most part solved.
However a disadvantage with this type of biometric authentication chip card is its complexity, and consequently its cost. Indeed, the mathematical treatment for the signature determination and for the comparison is complex, and requires a high degree of calculating power and substantial means of memorization, which are hardly compatible with the objectives of low-cost mass production, and with the dimensions of a chip card or of any other portable object.
Another disadvantage of this approach, from a security standpoint, is that the chip card constantly contains the reference signature, which an ill-intentioned third party could attempt to extract, for example after having stolen the card.